When you play this, you draw a card and get +2 Actions.
If this is trashed, you take it from the trash and put it into your
hand. This happens no matter whose turn it is when Fortress is
trashed. It is not optional. You still trashed Fortress, even though
you get it back; for example if you play Death Cart and choose to
trash Fortress, the "if you do" on Death Cart is true, you did trash
an Action, so you do not trash Death Cart.